Our ability to selectively focus attention on elements of our sensory environment is a critical cognitive function that enables us to enhance the processing of high priority stimuli. A classic example is the "cocktail party" effect, in which a person can focus selectively on a particular speaker while tuning out other conversations. In vision, attending to a particular region of the visual field results in faster and better detection and discrimination of stimuli in that region. Both electrophysiological and hemodynamic brain imaging studies have shown that top-down executive attentional mechanisms can influence early sensory processing in modality-specific cortices. Recent studies using event-related functional MRI (fMRI) in humans have implicated a fronto-parietal network in the executive control of visual attention. As yet, however, relatively little work has investigated how attention is switched or coordinated between sensory modalities. Thus, it is not yet clear which brain mechanisms, regions, and resources controlling attention are supramodal and which are modality specific. Moreover, real objects, including speakers at cocktail parties, have multisensory characteristics that need to be attended, perceived, and integrated. Because multisensory integration involves synthesis of information derived from different sensory channels, it is not clear that the same attentional mechanisms will be operative in a multisensory environment as are employed in a unisensory situation. For example, attention to one feature or aspect of a multisensory object (e.g., the face of a speaker) might lead to a cross-modal spreading of attention (e.g., to encompass the speaker's voice). The present project proposes to combine event-related potentials (ERPs) and event-related fMRI to study the mechanisms by which attention operates in multisensory environments. This will include the study of executive control mechanisms and brain circuits that coordinate and switch attention between different sensory modalities, as well as how attention influences and interacts with the processing and integration of multisensory stimuli. Recording both ERP and fMRI measures of brain activity during the attentional tasks will reveal not only the brain areas that subserve multisensory attentional operations, but also the timing and sequence of their activations, thereby enhancing our understanding of the underlying mechanisms. Attentional deficits form key components of a variety of neurological disorders and mental illnesses, and thus elucidating the basic mechanism.